^To be fair, it has happened a few times. Notably Six Flags Magic Mountain in 2011 (their 40th) when they opened backwards Superman, Green Lantern, and Road Runner Express. But then again, if any park in the world were to celebrate anniversaries with a new coaster, it would be SFMM. And barring any delays, I can totally see them celebrating their 50th next year with that new Jersey Devil clone.
But in general, yeah, anniversaries definitely do not correlate to new coasters that year.
Steel: 197 / Wood: 33 / Total: 230
Home Parks: Knott's (when home), Lagoon (at school)
Favorite Coaster: Intimidator 305